When this issue happens, it is mainly when I am doing sirenes. Feels like i take in a lot of air, but Im not sure. Maybe I hold the siren too long, thus running out of air?
Have you experienced the same thing yourself?

I can relate to what you are saying, it might be caused by pulling to much weight up high. I can actually sing with much lighter weight above A4, not experiencing the same issues. So i might go easier on the high notes for a while.
However it is also interesting to sing high notes with full weight, certainly you have male singers who can do this. I guess you have to push your limits at some point, to be able to do that.

Ive been encountering a surprising problem lately. When I sing sustained high notes (typically from B4 and higher), I get what feels like blood pumping in my brain immediately afterwards. Very painful, and I am also considering that this may not be very healthy. Any other singers experiencing this problem?

When you say TA strength, do you mean chest voice muscle strength?
I actually started to get some quite nice belting tones, especially for the AH, and the other vowels are getting better. However, i find it very hard to say something else up there other than those vowels, so it is not really that effecting if there are words and sentences above E4. Hehe

Im not trying to say that I want to sing full chest when I am performing, but it seems like good singers are able to do so if they like. Maybe increased flexibility in the chest voice allows for more upper control like easier light chest engagement when in the head voice. Thats why it might be interesting to actually develop a quite flexible chest voice, of course without disregarding the training the other aspects of the voice.

Yoyo!
I recently watched this seriously awesome video, by the forum member Jens. Great demonstration and clarification of registers, as well as some wise words on developing all the parts of the voice. I have noticed that several of the forum members that can sing and have proven so by posting videos of themselves singing, can take their full chest voice quite high (even as high as C5 as Jens said). It seems like having a flexible chest voice can be very beneficial, for example when singing sentences above your passagio, or when connecting back down to chest from head (or mix).
So my question is: How to train the chest voice to go up as high as B4, C5 etc?
I have previously made an attempt at stretching the chest with method 3, and I will try to post a demonstration tomorrow.
To me, it seems like there are two or three main ways to go about it
1. Develop chest voice by singing where it is comfortable.
2. Develop chest voice by singing high chest voice lightly.
3. Develop chest voice by pulling back (no straining) and drag it up as far as possible.
Any thoughts on this subject? What have worked in your experiences?
Important here to clarify that the question is about developing the chest voice to reach higher notes, not development of the chest voice in its comfortable register.
Video by Jens:
https://www.youtube.com/watch?v=uoknlqiaryo&index=13&list=LLSF6n64Wu9_EzUw8Ragt_Cg

I been putting a lot of thought into how often you should work your voice. Obviously there is both a muscular and a technical aspect of your singing. From athletic experience of working out and building muscles, its pretty much agreement that it takes 48 hours to completely recover a trained muscle. However, i guess we are not training the biggest muscles when doing vocal warm-ups, so you might argue that you can train your voice more frequently. What are you guys experience with this? How often to you sing/train your voice? With how much intensity? How are youre results with this frequency of "vocal workouts"?